Work from this laboratory has demonstrated the mechanism adenine and adenosine transport in E. coli as well as the relationship between uptake regulation and the amino acid control of nucleic acid synthesis in this species. We would now like to extend these studies to determine whether the multiple forms of the enzyme(s) we have been able to purify having 6-OH purine phosphoribosyltransferase activity have more limited substrate specificity in situ in the membrane than in the purified soluble form. Though the enzyme will accept all 6-OH purines in aqueous solution, transport of these purines is differently and completely dependent on the presence of a particular enzyme form in the membrane. Mutational losses totally effect either hypoxanthine or guanine utilization though there is always residual enzymatic activity in extracts for both substrates. Our studies will be aimed at further elucidating the mechanism of purine uptake and its regulation in enteric bacteria, especially with regard to guanine and hypoxanthine where our understanding is not as complete as it has become for adenine. We also intend to investigate the basic relationship of the role of the membrane on enzyme function and vice-versa using this multifaceted system whose regulation has many components. Our techniques will include enzyme purification, membrane transport and genetic analysis.